1. Field of the Invention
The invention related to processes for the hydrohalogenation of myrcene.
2. Brief Description of the Prior Art
The literature is replete with descriptions of processes for the hydrohalogenation of conjugated dienes. Representative of such descriptions are those found in the U.S. Pat. Nos. 2,882,323 and 3,016,408 and in British Pat. No. 896,262; see also German Offenlegungsschrift 1,768,544. In the latter patent, hydrohalogenation of butadiene is conducted in the presence of aqueous mixtures including organic amines. The reaction mixtures are corrosive and in some reactions would tend to promote solvolysis. The German Auslegeschrift 1,253,264 describes the hydrochlorination of butadiene in a gas phase reaction. The present invention is an improvement over the prior art processes in that it may be carried out in liquid phases of the reactants, at low temperatures and with minimal solvolysis of products. Improved yields are obtained of the desired products.
The present invention is advantageous when used to hydrochlorinate myrcene. Myrcene is a conjugated diene of the formula: ##STR1## When hydrochlorinated in the absence of any catalyst, the major product is myrcenyl chloride. However, the commercially valuable products of myrcene hydrochlorination are the associated co-products, namely, geranyl chloride and neryl chloride. Hydrochlorination in the presence of a copper-containing catalyst shifts the reaction in favor the desired co-products. It has been postulated that the hydrochlorination of myrcene in the presence of a copper catalyst proceeds according to the reaction scheme: ##STR2## Cyclization may also undesirably occur to form the alpha-terpinyl chlorides, especially at reaction temperatures in excess of 25.degree. C.
When the copper catalyst employed is in the form of cupric chloride (CuCl.sub.2) the products generally include substantial proportions of linalyl chloride and lesser proportions of the desired geranyl and neryl chlorides. When the copper catalyst is in the form of cuprous chloride, the linalyl chloride product is lessened due, apparently, to partial isomerization to the desired geranyl and neryl chlorides.
From the above proposed reaction scheme, it will be appreciated that any process for hydrochlorination of myrcene, to be commercially feasible, must result in a favorable yield of the desired geranyl (II) and neryl (III) monochlorides and minimal formation of linalyl (IV) and alpha-terpinyl (VI) monochlorides. It was previously appreciated that the relative proportions of monochlorides (II), (III) and (IV) in the hydrochlorination product reaction mixture could be controlled to some degree by selection of the reaction temperature, gas flow-rate and catalyst concentration.
We have now found that when the prior art hydrohalogenation of myrcene (U.S. Pat. No. 2,871,271), is carried out in the presence of a particular kind of organic amine, then the isomerization of the linalyl chloride product during the hydrohalogenation reaction is shifted to favor formation of the less-substituted allylic chloride, being geranyl chloride (II) and neryl chloride (III).
While it is known to include certain organic amines in combination with copper in a catalyst for hydrochlorination of a simple diene such as butadiene (U.S. Pat. No. 3,993,586 to Hagedorn, et al), these amines fail to increase the yield of neryl and geranyl halides when applied to the hydrohalogenation of myrcene, even when used under anhydrous conditions. It is also known that certain organic amines can be employed in combination with copper to isomerize allylic halides to their allylic isomers (British Pat. No. 798,889 to Young), but only at elevated temperatures. These amines also fail to increase the yield of neryl and geranyl halides when applied to the hydrohalogenation of myrcene, even when used at the lower temperatures necessary in this reaction to avoid extensive yield losses due to rearrangement to terpinyl halides.
The advantages associated with the improved process of the invention include improved overall yield of the more desirable neryl and geranyl chlorides from myrcene and a greater selectivity of the more important geranyl isomer.